FIELD OF THE INVENTION AND PRIOR ART
The present invention relates to a set of devices for transferring electric signals. Each device comprises a first unit having a bus and means for electrically and mechanically connecting the bus to a bus of another of the devices for connecting the devices to each. Each device further comprises a second unit having terminals for an external connection of the device to electrical arrangements for signal exchange with the electrical arrangements. Each device further comprises a signal adapting module electrically connected to the bus through a connection and to the terminals through a connection, and thereby electrically connecting the bus and the terminals.
Such devices may be of different types and are used for different types of signal transfer, both of numerical and analog character. Signals arriving to the bus of the device, for example from a central unit are after a signal adaptation in the signal adapting module, emitted through a terminal to different electrical arrangements for their control. Signals from the electrical arrangements also pass through signal adaptation in the signal adapting module. For example, analog signals arriving to the bus of the device through the terminals after conversion to numerical signals may be measuring signals from any pressure, temperature or flow sensor. The analog output signal may then be sent to an arrangement for controlling a regulator, for example a valve regulating a flow, or a means regulating the temperature of an oven. Signals arriving to the bus of the device may, in the case of numerical signals, derive from signal contacts or electrical components similar thereto, while signals from the signal adapting module to the terminals may control, for example, a motor through a contactor. The bus may also allow communication between different devices connected to each other and a central unit. The devices or the electrical arrangements connected thereto may also receive their power supply through the bus.
The space requirement for such a device of is strongly dependent upon how many terminals the device has to have. there are devices of two main types which demand much space for connection to a determined number of electrical arrangements.
The first main type is generally called "minimum termination device", and it has substantially the same number of terminals as the number of electrical arrangements to be connected thereto, normally one terminal per signal, plus one or two terminals for power supply, which the arrangements have in common. Such a device may be compact and demands little space, but it has the disadvantage that a number of electrical components have to be arranged outside the device between the latter and the electrical arrangements. Further, an extended arrangement of cables will be necessary, since the electrical arrangements each require two or more terminals. Such electrical components may, for example, be different types of switching means, circuit breakers, components setting conditions, terminals and so on. It is not possible to connect more than a few arrangements, each requiring two or more terminal connections or connection interfaces, to such a device.
Devices according to the second type have more than one terminal for the same number of arrangements as devices according to the first type only have one terminal for, and They may also have electrical components incorporated into the signal path between the signal adapting module and the terminals. This has the advantage that no such electrical components have to be arranged outside between the device and the electrical arrangements, which results in a considerably simpler arrangement of cables. Such a device requires more space than devices of the first type, since it has more terminals, often three terminals per arrangement.
A disadvantage of sets of devices either of the first type or of the second type is being locked into a determined connection interface, which may mean that the connection interface for some devices is unnecessarily large, and the device in question thus requires more space than should be necessary. Or that the connection interface is too small to enable connection of the electrical arrangements desired to a given device in a desired way.